Rotary tools employing wear-resistant cutters are conventionally utilized in a variety of drilling, cutting, and machining operations. For example, superabrasive and/or superhard materials, such as polycrystalline diamond (“PCD”) or ceramics (e.g., cubic boron nitride, silicon carbide, and the like), are often used in drilling tools, machining equipment, and in other mechanical systems. Cutting elements are often employed on earth boring rotary drill bits, such as roller cone drill bits and fixed-cutter drill bits used for drilling subterranean formations. A rotary drill bit may include one or more cutting elements affixed to a bit body of the rotary drill bit.
Conventional earth boring drill bits may include a bit body formed from steel or a hard matrix material, such as tungsten carbide. Cutting elements are typically positioned along leading edges or surfaces of the bit body so that the cutting elements engage and drill earth formations as the bit body is rotated in its intended direction of use. The cutting elements may be positioned and secured in recesses formed in an exterior of the bit body. Depending on the bit body design, cutting elements may either be positioned in a mold prior to formation of the bit body or secured to the bit body following fabrication.
A steel bit body is often machined from round steel stock to a desired shape. Various surface features, such as blades and/or junk slots, and internal features, such as fluid passages for delivery of drilling fluid, may be machined into the bit body using a machine tool. An end of the bit body may then be welded and/or otherwise secured to a shank, such as a threaded steel shank. During use in drilling operations, the shank may secure the drill bit to a corresponding connection point, such as a threaded connection on a drill string.
A bit body formed from a hard matrix material is generally formed by packing a graphite mold with tungsten carbide powder, and subsequently infiltrating the powder with a molten copper alloy binder, such as brass. A drill bit “blank” comprising steel or other suitable material may be positioned in the mold so that the blank becomes securely fixed to the matrix upon cooling. The blank may be generally cylindrical or may include various surface features, such as blades and/or junk slots. A mandrel may also be positioned in the mold and subsequently removed after molding and furnacing, leaving behind fluid passages in the drill bit for conveyance of drilling fluid to the cutting surfaces. After the bit body has been molded, the end of the steel blank may be secured to a threaded shank.
During production of drill bits, numerous factors may result in imperfections in the external shape of the drill bit leading to inconsistent and/or sub-optimal performance of the drill bit during drilling. In molding processes, even slight changes in processing conditions may result in significant alterations in the shape and performance of the finished product. For example, during molding operations, various conditions, such as humidity, processing temperatures, and/or rates of heating and/or cooling may result in different rates of expansion and/or shrinkage of a molded bit body during processing of the molded part. The compositions of materials used in the molding process may also affect the finished part.
Removal of material during drilling is performed by the cutting elements located radially around the bit body. In conventional drill bits, the cutting elements may be positioned strategically to establish the maximum performance in removing material during downhole drilling. The orientation of the cutting elements may establish a cutting element rotational axis that differs from the bit body rotational axis due to various imperfections in the drill bit, such as manufacturing imperfections as mentioned above. The cutting element rotational axis may be determined by the final placement of the cutting elements relative to one another, their placement on the bit body, and locations of surfaces regions of the cutting elements relative to one another and the bit body.
Additionally, during drilling operations, the bit body and cutting elements may be exposed to significant abrasive and erosive forces, causing changes in the exterior shape of the drill bit. As the drill bit experiences wear, the performance of the drill bit tends to decrease. Cutting elements on the drill bits are typically subjected to the greatest amount of wear during drilling. Accordingly, the cutting elements may need to be replaced long before the bit body. Conventionally, worn cutting elements are removed from the bit body and replaced by new cutting elements, which are secured to the old bit body.
Subsequently, the new cutting elements may be machined so that they extend to a desired distance relative to the bit body. For example, cutting elements protruding radially outward from the bit body may be ground using a grinding machine so that the drill bit is sized to fit within a borehole having a certain diameter. A grinding machine conventionally used for grinding cutting elements mounted on a drill bit requires the drill bit to be manually loaded in the grinding machine so that the drill bit extends in a substantially horizontal direction. A grinding wheel that is rotated about a generally horizontal axis is then used to grind the cutting elements to specified depths to ultimately achieve the desired diameter of the outer bit cutting elements relative to the bit body.
Following manufacturing of new drill bits or machining of used drill bits, conventional measurement tools may be used to determine whether certain characteristics of the drill bits are within specified tolerances. However, such measurement tools are often incapable of determining various characteristics affecting the performance of the drill bits during operation. For example, gauge rings are conventionally utilized to determine whether the outer diameter of a drill bit lies within a specified range, ensuring that the drill bit is sized to fit within a borehole having a specified diameter. While the gauge rings can determine the general diameter of the drill bit, they typically cannot be used to accurately determine a rotational axis of the drill bit body or the rotational axis of the cutting elements.
A drill bit having an outer diameter that is not centered about the cutting element rotational axis or the bit body rotational axis may perform in an inconsistent or undesirable manner during drilling. Drill bits not operating around the cutting element rotational axis will seek and track the cutting element rotational axis regardless of the bit body rotational axis. For example, if a drill bit is not sufficiently centered about the cutting element rotational axis, there may be significant skipping or rifling of the drill bit in the borehole as the drill bit seeks the cutting element rotational axis. Even small differences in the shape or alignment of a drill bit may significantly affect the performance of the bit. Sub-optimal performance of drill tools, such as drill bits, may cause decreased performance efficiency during drilling operations, premature damage to bit bodies and cutting elements, and lost costs and labor productivity due to unnecessary repairs and part changes.